Community dynamics and trophic niches of soil fauna in Central European forests
by André Junggebauer
Date of Examination:2024-08-27
Date of issue:2024-09-06
Advisor:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Andreas Schuldt
Referee:Prof. Dr. Mark Maraun
Referee:Prof. Dr. Christoph Bleidorn
Referee:Prof. Dr. Christian Ammer
Referee:Dr. Sven Bradler
Persistent Address:
http://dx.doi.org/10.53846/goediss-10712
Files in this item
Name:PhD_Thesis_AJ_noCV.pdf
Size:5.10Mb
Format:PDF
The following license files are associated with this item:
Abstract
English
Global change is altering the state of forest ecosystems, threatening their integrity. A number of studies have reported declines in aboveground arthropod diversity over the last decade and indicated management practices or climate as the main drivers. However, belowground communities have rarely been studied in this context, and the extent to which patterns and associated drivers observed aboveground also apply to belowground communities remains unknown. Therefore, research is urgently needed to disentangle the drivers and potential threats that shape soil animal communities, which contribute significantly to the functioning of terrestrial ecosystems by providing key ecosystem functions such as decomposition and nutrient cycling. Here, we studied soil animal communities across forest types of different management intensity, including unmanaged beech forests, managed age-class beech forests and spruce monoculture plantations across three regions located in southern, central, and northern Germany, i.e., Swabian Alb, Hainich-Dün, and Schorfheide-Chorin. We first investigated the spatiotemporal dynamics of oribatid mites (Acari: Oribatida), sampled in three-year intervals from 2008 – 2020 (Chapter 2). In contrast to the linear decline in diversity observed aboveground, oribatid mite density and diversity decreased after years with low preceding winter precipitation and recovered after years with higher precipitation. This correlation differed between regional soil types and was only found in the Swabian Alb and Schorfheide-Chorin, where soil fauna is more susceptible to periodic droughts due to the shallow Rendzinas and sandy soils, respectively. Temporal dynamics were similar between managed and unmanaged forests, suggesting that forestry has little effect on the viability of oribatid mite populations in Central European forests. To gain a more mechanistic understanding of the effects of extensive forest management, we then examined oribatid mite communities one year after two key characteristics of forest management; namely forest gap formation and deadwood availability were manipulated in a full factorial experiment (Chapter 3). We found that both deadwood and forest gap formation significantly affected oribatid mite density and community composition, although the magnitude of these effects differed between regions. One year after deadwood addition, oribatid mite density approximately doubled in the Hainich-Dün, mainly due to a few fast-reproducing species. Presumably, they benefitted from additional microbial resources near deadwood, particularly fungi, which are the prime resource of oribatid mites as shown in Chapter 4. By contrast, forest gap formation reduced the density and diversity of oribatid mites but only in the Swabian Alb and Schorfheide-Chorin. Given the strong correlation between oribatid mite density and precipitation found in these two regions in Chapter 2, it is likely that periodic droughts were aggravated in forest gaps, adversely affecting oribatid mite communities. Notably, negative effects of forest gap formation were not mitigated by the addition of deadwood, indicating that harsh environmental conditions override the positive effects of additional resources. Finally, we linked the dynamics of soil animal communities to their function in the soil food web by analyzing trophic niches of detritivores (Oribatida, Collembola, Diplopoda, Isopoda, Lumbricidae) and predators (Mesostigmata, Chilopoda) across forest types and regions. Trophic niches were derived by analyzing the relative contribution of plants, fungi, and bacteria used as basal resources and estimating trophic positions, using community-level compound-specific stable isotope analysis of amino acids (Chapter 4). Results showed that soil animal detritivores in forests mainly feed on fungi, followed by plants and to a lesser extent on bacteria. Relative proportions of basal resources were consistent across forest types and regions for all taxa. Notably, Chilopoda obtained more essential amino acids from bacteria than other investigated taxa, suggesting that they prey on soil animals not included in the study. Enchytraeidae are known to serve as prey for Chilopoda and have recently been shown to feed on bacteria. Trophic positions were higher in the Schorfheide-Chorin for Oribatida and Collembola but decreased for Lumbricidae. This may in part be related to regional differences in community composition, as shown for oribatid mites in Chapters 2 & 3. Also, increasing trophic positions suggest longer trophic chains, which may be explained by the integration of more root-derived resources and/or rhizosphere prey, due to higher root density in the organic layers of sandy soils. The results of this thesis show that the dynamics of oribatid mite communities are little affected by forest management and are mostly determined by abiotic conditions at regional scales. However, more extensive forest management events, such as the formation of forest gaps, may interact with regional abiotic stressors, leading to aggravated effects on oribatid mites. The thesis also provides the first evidence that fungi are the main resource for mesofauna and macrofauna detritivores and that trophic niches in soil are conserved between forest types of different management intensity. Future studies need to assess the generality of these findings and further explore the complex interactions between forest management practices and regional abiotic factors.
Keywords: Forest management; Belowground diversity; Oribatid mites; Trophic niches; Temporal stability; Soil fauna
